The present invention relates to a magnetic recording medium and method for manufacturing the same.
Lately, there has been a remarkable advancement in a field of mechatoronics of automobiles, machine tools, and the like. Especially in the field of mechatronics of automobiles, it has been desired to develop a technique for measuring a torque of a shaft member used for various parts of the automobile, a rotating speed, or rotating angle of the shaft member with high precision.
There is known a method for detecting a torque of the shaft member, utilizing a magnetic characteristic of a magnetic film which is formed on the shaft member. For example, a magnetoristriction method (a stress - magnetic moment effect) of the film is utilized for detecting the torque. In this method, the precision of detected torque is affected by the magnetic characteristic of the film. Namely, the characteristic of the magnetic film changes when a temperature changes or time passes. Consequently, the magnetostriction method has not been fully put to practical use.
On the other hand, the torque detecting method based on a torsional angle of the shaft member is also known. In this method, a magnetic signal of rectangular pulse is recorded by a magnetic recording head to the magnetic film formed on a surface of the shaft member. Then, the magnetic signal is regenerated by a magnetic signal regenerating head so as to obtain the torsional angle of the shaft member. And the torque of the shaft member is calculated based on the torsional angle.
There is known a method for manufacturing a magnetic scale of an encoder for detecting a rotating speed, by spraying a molten magnetic material on a surface of a base piece to form a magnetic film (refer to Japanese Patent Application Laying Open Gazette No. 61-53504).
In order to put the magnetic recording medium to practical use, a magnetic characteristic of the magnetic film becomes an essential key when using a head for recording and regenerating the signal to the magnetic film in the torque detecting method based on the torsional angle.
Namely, when a coercive force of the magnetic film is high, it is difficult to record the magnetic signal, the head is damaged by a heat, and its durability is lowered because an output of the head is required to be raised. On the other hand, if the coercive force is low, the recorded magnetic signal is easily erased. This leads to a lowering of a regenerated output. If a saturation magnetization or a residual magnetization of the magnetic film is raised, the regenerated output can be raised and if the saturation magnetization and the residual magnetization are lowered, a recording frequency for the magnetic signal can not be increased.